The present invention relates to fluid discharging method and device for very small flow rates required in such fields as information/precision equipment, machine tools, and FA (Factory Automation), or in various production processes of semiconductors, liquid crystals, displays, surface mounting, and the like.
For liquid discharging devices (dispensers), which have hitherto been used in various fields, there has arisen a growing demand for a technique of feeding and controlling very small amounts of fluid material with high precision and high stability, against the background of recent years' needs for smaller-size electronic components and higher recording density. For example, in the fields of plasma displays, CRTs, organic EL, or other displays, there has been a great demand for direct patterning of fluorescent material or electrode material on the panel surface without any mask instead of conventional screen printing, photolithography, or other like methods.
Issues of dispensers for those purposes can be summarized as follows:    {circle around (1)} Scale-down of application amount,    {circle around (2)} Higher accuracy of application amount, and    {circle around (3)} Reduction of application time.
The machining accuracy in machining work has been moving from micron into submicron orders. Whereas the submicron machining is commonly used in the field of semiconductor and electronic components, the demand for ultraprecision machining has been rapidly increasing also in the field of machining work that has been making progress along with mechatronics. In recent years, along with the introduction of the ultraprecision machining technique, electromagnetostriction devices typified by ultra-magnetostriction devices and piezoelectric devices have been coming to be applied to micro actuators. With one of these electromagnetostriction devices used as a generation source for fluid pressure, there has been proposed an injection device for injecting very small amounts of droplets at high speed. For example, a method of injecting one arbitrary droplet with an ultra-magnetostriction device is disclosed in Unexamined Japanese Patent Publication No. 2000-167467. Referring to FIG. 24, reference numeral 502 denotes a cylinder made of a nonmagnetic material such as glass pipe or stainless pipe. At one end portion of this cylinder 502 is formed an injection nozzle 504 having a liquid storage portion 503 and a minute injection port. Inside the cylinder 502, an actuator 505 made of a bar-shaped ultra-magnetostriction material is accommodated so as to be movable. A piston 506 is contactably and separably provided at an end portion of the actuator 505 suited for the injection nozzle 504.
Between the other end portion of the actuator 505 and a stopper 507 of the one end portion of the cylinder 502, a spring 508 is interposed so that the actuator 505 is biased by the spring 508 so as to be moved forward. Also, a coil 509 is wound at a position near the piston 506 on the outer periphery of the cylinder 502.
In the injection device having the above construction, a current is instantaneously passed through the coil 509 so that an instantaneous magnetic field acts on the ultra-magnetostriction material, by which an instantaneous transient displacement due to an elastic wave is generated at an axial end portion of the ultra-magnetostriction material. By the action, it is described, the liquid filled in the cylinder 502 can be injected from the nozzle 504 as one minute droplet.
As the dispenser, conventionally, such a dispenser employing the air pulse system as shown in FIG. 25 has been widely used, and this technique is introduced, for example, in “Jidoka-Gijutsu (Mechanical Automation), Vol. 25, No. 7, '93” etc.
A dispenser of this system applies a constant mount of air supplied from a constant-pressure source into the interior 601 of a vessel 600 (cylinder) in a pulsed manner and then discharges from a nozzle 602 a certain amount of liquid corresponding to a pressure increase in the cylinder 600.
With an aim of high-speed intermittent application, such a dispenser as shown in FIG. 26 (hereinafter, referred to as “jet system” for convenience' sake) has already been put into practice. Reference numeral 550 denotes a micrometer, 551 denotes a spring, 552 denotes a seal member of the piston, 553 denotes a piston chamber, 554 denotes a heater, 555 denotes a needle, 556 denotes an application material flowing toward a sheet portion, and 557 denotes a dot-shaped application material which flies from the dispenser. FIGS. 27A and 27B are model views showing a discharge portion proximity 558 of FIG. 26, where FIG. 27A shows a suction process and FIG. 27B shows a discharge process. Numeral 559 denotes a spherical-shaped convex portion 559 formed at a discharge-side end portion of the needle 555, 560 denotes a discharge tip portion, 561 denotes a spherical-shaped concave portion formed at this discharge tip portion 560, and 562 denotes a discharge nozzle. Numeral 563 denotes a pump chamber formed by the spherical-shaped convex portion 559 and concave portion 561.
Referring to FIG. 27A, which shows a suction process, when the feed air pulse of the piston chamber 553 is ON, the needle 555 moves up against the spring 551. In this case, a suction portion 564 formed between the spherical-shaped convex portion 559 and concave portion 561 is opened, an application material 556 is filled from the suction portion 564 into the pump chamber 563. Referring to FIG. 27B, which shows a discharge stroke, when the air pulse is OFF, i.e., when no air pressure is applied to the piston chamber 553, the needle 555 is moved down by the force of the spring 551. In this case, the suction portion 564 is shielded, and the fluid within the pump chamber 563 is compressed by the tightly closed space excluding the discharge nozzle 562, thus generating a high pressure and making the fluid fly and flow out.
There has been being made development for applying the ink jet system, which has been widely used as consumer printers, to application devices for industrial use. Referring to FIG. 28, which shows a prior art example of a head portion in an ink jet recording device (Unexamined Japanese Patent Publication No. 11-10866), numeral 651 denotes a base, 652 denotes an oscillation plate, 653 denotes a stacked-type piezoelectric element, 654 denotes an ink chamber, 655 denotes a common ink chamber, 656 denotes an ink flow passage (throttle portion), 657 denotes a nozzle plate, and 658 denotes a discharge nozzle. When a voltage is applied to the piezoelectric element 653, which is a pressure applying means, the piezoelectric element 653 makes the oscillation plate 652 deformed thicknesswise, causing the ink chamber 654 to be decreased in capacity. As a result, the fluid is compressed so that the pressure of the ink chamber 654 increases, causing a part of the fluid to pass through the ink passage 656 and reversely flow toward the common ink chamber 655 while the rest of the fluid is discharged out to the atmosphere from the discharge nozzle 658.
In the field of circuit formation, or in the fields of electrodes, ribs, and fluorescent-screen formation of PDP, CRT, or other image tubes, and manufacturing processes of liquid crystals, optical disks, organic EL, or the like, where higher precision and higher micro-fineness have been increasingly demanded for those fields in recent years, the fluid material to be micro-finely applied is high-viscosity powder and granular material in many cases. For replacement of conventional methods with a direct patterning method using dispensers, the greatest issue is how it can be practicable that very small amounts of high-viscosity powder and granular material containing fine particles having mean outside diameters of several microns to several tens of microns, exemplified by fluorescent material, electrically conductive capsules, solder, and electrode material, are micro-finely applied onto the object substrate at high speed and high precision and without causing clogging of flow passages and moreover with high reliability.
With regard to the fluorescent material-layer forming process of plasma display panels as an example, issue of the prior art are described below.
<1> Issues of Screen Printing Method and Photolithography Method
<2> Issues in Direct Patterning of Fluorescent Material Layer by Conventional Dispenser Technique
First, the issue <1> is explained.
(1) Construction of Plasma Display Panel
FIG. 29 shows an example of the construction of a plasma display panel (hereinafter, referred to as PDP). The PDP is composed roughly of a front side plate 800 and a rear side plate 801. A plurality of sets of linear transparent electrodes 803 are formed on a first substrate 802, which is a transparent substrate forming the front side plate 800. Also, on a second substrate 804 forming the rear side plate 801, a plurality of sets of linear electrodes 805 are provided parallel to one another so as to be perpendicular to the linear transparent electrodes. These two substrates are opposed to each other with interposition of barrier ribs 806 on which the fluorescent material layer is formed, and then discharge gas is sealed into the barrier ribs 806. When a voltage not lower than the threshold is applied to between the two substrates, electric discharge occurs at the positions where the electrodes perpendicularly cross each other, causing discharge gas to emit light, where the light emission can be observed through the transparent first substrate 802. Then, by controlling the discharge positions (discharge points), it becomes possible to display an image on the first substrate side. For color display by PDP, fluorescent materials which emit light of desired colors by ultraviolet rays radiated upon discharge at individual discharge points are formed at positions corresponding to the discharge points (partition walls of barrier ribs), respectively. For full-color display, fluorescent materials for R, G, and B, respectively, are formed.
The constitution of the front side plate 800 and the rear side plate 801 is explained in more detail.
As to the front side plate 800, a plurality of sets of linear transparent electrodes 803, each one set comprising two electrodes, are formed from ITO or the like, parallel to each another, on the inner surface side of the first substrate 802 formed of a transparent substrate such as a glass substrate. Bus electrodes 807 for reducing the line resistance value are formed on the inner-side surfaces of these linear transparent electrodes 803. A dielectric layer 808 for covering those transparent electrodes 803 and bus electrodes 807 is formed all over the inner surface of the front side plate 800, and a MgO layer 809 serving as a protective layer is formed all over the surface of the dielectric layer 808.
On the other hand, on the inner surface side of the second substrate 804 of the rear side plate 801, a plurality of linear address electrodes 805 which perpendicularly cross the linear transparent electrodes 803 of the front side plate 800 are formed in parallel from silver material or the like. Also, a dielectric layer 810 for covering those address electrodes 805 is formed all over the inner surface of the rear side plate 801. On the dielectric layer 810, the address electrodes 805 are isolated and moreover the barrier ribs (partition walls) 806 of a specified height are formed so as to protrude between the individual address electrodes 805 for the purpose of maintaining the gap distance between the front side plate 800 and the rear side plate 801 constant. With these barrier ribs 806, cells 811 are formed along the individual address electrodes 805, and fluorescent materials 812 of respective R, G, and B colors are formed one by one in the inner surfaces of the cells 811. The PDP in cell structure comes in two types, one in which such discharge points as shown in FIG. 29 are provided one in each one independent cell and the other in which the discharge points are partitioned by partition walls on an array basis (not shown). In recent years, the “independent cell system” has been drawing attention as a system that allows performance improvement of PDPs. The reason of this is that enclosing the cell with four-side barrier ribs in a waffle-like state makes it possible to prevent optical leakage between adjoining cells as well as to increase the area of the light emitter. As a result, the luminous efficiency and the emission amount (brightness) are increased so that a high-contrast image can be implemented, which is regarded as a characteristic of the “independent cell system”. The fluorescent material layer formed on the cell wall surfaces is deposited generally to a thickness of about 10–40 μm with a view to better coloring property. For the formation of the R, G, and B fluorescent material layers, a fluorescent-material use coating liquid is filled into each cell and thereafter dried, thereby making volatile components removed, by which a thick fluorescent material is formed on the cell inner surface while a space for filling the discharge gas is formed at the same time. In order to form such a thick-film fluorescent-material pattern, the coating material containing a fluorescent material is prepared as a reduced-in-solvent-quantity paste fluid (fluorescer-member use paste) having a high viscosity of several thousands of mPas to several tens of thousands of mPas and, conventionally, applied to the substrate by screen printing or photolithography.
(2) Issues of Conventional Screen Printing Method
With the conventional screen printing method adopted, a large-scaled screen size would cause a large elongation of the screen plate due to tensile force, making it harder to achieve high-precision alignment of the screen printing plate for the whole screen. Also, in filling the fluorescent material, the material might be placed even on the top portions of the partition walls, which would lead to crosstalk between barrier ribs as a problem in the case of the “independent cell system”. As a result of this, it has been necessary to take measures such as introduction of a polishing process for removing the material deposited on the top portion. Further, since the amount of filled fluorescent material varies depending on the difference in squeegee pressure, pressure control therefor is extremely subtle work, which largely depends on the degree of the skill of the operator. Thus, it is quite hard to obtain a constant filling amount for every independent cell over the entire rear side plate.
(3) Issues of Conventional Photolithography
The conventional photolithography PDP method has had the following issue. In this method, a photosensitive fluorescent-material use paste is press-fitted into the cells between the ribs, and then only the photosensitive composition that has been press-fitted into specified cells is left through exposure and development processes. Thereafter, through a baking process, organic matters in the photosensitive composition are dissipated, by which a fluorescent material-layer pattern is formed. In this method, in which the paste in use contains fluorescent-material powder so that the method is low in sensitivity to ultraviolet rays, there has been a difficulty in obtaining a 10 μm or more film thickness of the fluorescent material layer. Thus, the method has had an issue that enough brightness cannot be obtained.
Also, in the case where photolithography is adopted, exposure and development processes are essential for each color. However, since the fluorescent material is contained in the paste coating layer at high concentration, the loss of the fluorescent material due to the development removal is such large that the effective utilization ratio of the fluorescent material is a little less than 30% at most. Thus, there has been a large issue in terms of cost.
<2> Issues in Direct Patterning of Fluorescent Material Layer by Conventional Dispenser Technique
(1) Issues of Air Nozzle Type Dispenser
Conventionally, an attempt is made that coating of the imaging tube is performed by using an air nozzle-type dispenser (FIG. 25) which is widely used in the fields of circuit mounting and the like. Since continuous application with high-viscosity fluid at high speed is difficult to do with the air nozzle-type dispenser, fine particles are diluted with a low-viscosity fluid before applied. In the case of fluorescent-material application on PDP, CRT, or other image tubes, the particle size of fine particles is 3 to 9 μm as an example and their specific gravity is about 4 to 5. In this case, there has been an issue that when the fluid flow is stopped, the fine particles would be immediately deposited inside the flow passage due to the weight of a single particle. Furthermore, the dispenser of the air type has had a drawback of poor responsivity. This drawback is due to the compressibility of air entrapped in the cylinder as well as to the nozzle resistance during the passage of air through narrow gaps. That is, in the case of the air type, the time constant of the fluid circuit that depends on cylinder capacity and nozzle resistance is such a large one that a time delay of about 0.07 to 0.1 second has to be allowed for after an input pulse is applied until the fluid is started being dispensed and further transferred onto the substrate.
The discharging device using as the drive source a piezoelectric material or ultra-magnetostriction material as described before in FIG. 24 is a proposal targeted for application of fluid containing no powder, and it is predicted to be difficult to respond to the aforementioned challenge related to the application process of powder and granular material. Also, in the case where a fluid is applied by using instantaneous transient displacement due to elastic waves, the liquid storage portion 503 has to be normally filled with the fluid without gaps, where the capacity is constant. There is no description as to, for example, how the fluid is supplied to the liquid storage portion 503 in order to replenish the fluid that is consumed on and on as time elapses.
(2) Issues of Jet Type Dispenser
The dispenser shown in FIG. 26 is enough fast in application speed, as compared with the air type, the thread groove type, and the like which are a prior art, and also capable of treating high-viscosity fluid. Also, this type of dispenser is capable of letting the fluid flown from the nozzle and intermittently applied while a sufficient distance is kept between the nozzle and its opposing surface. Such an application method that the fluid is let to fly from the nozzle is difficult to do with the air type and the thread groove type, both of which are incapable of producing an abrupt pulsed pressure.
This type of dispenser, as described before, is a method that a spherical-shaped convex portion formed at an end portion of the needle 555 and a spherical-shaped concave portion formed on the dispensing side are engaged with each other, thereby creating a tightly closed space 563 excluding the discharge nozzle 562, and this tightly closed space is compressed so that a high pressure is generated to let the fluid fly and flow.
In this case, in the compression process, the gap at the suction portion 564 between the relatively moving members (convex and concave portions) becomes zero, so that the fluorescent-material fine particles having mean particle sizes of 3 to 9 μm undergo a mechanical squeezing action, thereby broken. Because of various failures that would result therefrom, such as the clogging of the flow passage and deterioration of the sealing performance of the suction portion 564 due to wear of the members, it is difficult, in many cases, to apply this dispenser to powder and granular material application such as fluorescent material.
Another issue of this type of dispenser is to ensure application absolute-quantity precision per dot on a precondition of long-time continuous use. On the assumption that the fluorescent material is intermittently applied into the “independent cells” of the foregoing PDP, several tens of heads are necessary in consideration of the production cycle time in mass production. In this dispenser, the application quantity per dot is determined by the capacity of the tightly closed space, i.e. the stroke of the needle 555, and the sealing performance of the suction portion 564. However, it is predicted to be extremely difficult from the viewpoint of practical use to maintain the strokes and the absolute positions of individual needles 555 of the dispensers, Which are provided in a quantity of several tens, as well as the sealing performance of the suction portions 564 that is subject to wear, at a constant state for long time without variations.
(3) Issues of Ink Jet Type Dispenser
The ink jet type dispenser shown in FIG. 28, for which the viscosity of the fluid is limited to 10 to 50 mPas from the restrictions of drive method and structure, is incapable of treating high-viscosity fluids. Also, the particle size of the powder contained in the fluid is about 0.1 μm at most from the viewpoint of clogging.
In order to draw a fine pattern by using the ink jet type dispenser, there has been developed a low-viscosity nano-paste in which particles having a mean particle size of about 5 nm and covered with a dispersant are independently dispersed. Here is assumed a case in which a fluorescent material layer is formed on the inner wall of the barrier rib (partition wall) of the aforementioned PDP “independent cell” with the use of this nano-paste. However, in order that a 10 to 40 μm thick fluorescent material layer is deposited in the process of filling the fluorescent-material use coating liquid into the individual cells and thereafter drying the liquid, originally, a high-viscosity pasty fluid with a reduced amount of solvent is used as the coating material containing the fluorescent material, as described before. For a low-viscosity nano-paste that allows only a dilute content of fluorescent material to be contained therein, it is impossible to form a fluorescent material layer of a specified thickness because of its insufficient absolute quantity of fluorescent material. Also, whereas fluorescent-material fine particles having a micron-order particle size is commonly considered most suitable for the display to obtain high brightness, the ink jet type dispenser is incapable of easily changing the fluorescent-material particle size for the present stage, which is also a great issue of the ink jet type.
In summary of the above discussions, there cannot be found, for the present stage, a technical method having a capability of substituting for the screen printing method and the photolithography method, which is exemplified by a direct patterning method that implements the formation of an independent-cell fluorescent material layer for PDPs.
Now, proposals in the past relating to the intermittent-application dispensers by the present inventor are briefly explained. In order to meet the recent years' various requests related to the minute-flow-rate application, the present inventor has proposed and applied for patent a method for controlling the discharge amount of fluid, “Fluid Feeding Device and Fluid Feeding Method” (Japanese Patent Application No. 2000-188899, corresponding U.S. Pat. No. 6,558,127 and U.S. patent application Ser. No. 10/118,156), in which, with relative linear motion and rotational motion given to between a piston and a cylinder, fluid transporting means is implemented by the rotational motion while a relative gap between the fixed side and the rotation side is changed by using the linear motion.
This proposal is intended to control the interruption of the fluid by a dynamic sealing effect based on the arrangement that a thrust hydrodynamic seal is formed on a discharge-side end face of the piston and a relatively moving surface of its opposing surface, where the effect is produced when the gap between the opposing surfaces are narrowed.
In Japanese Patent Application No. 2000-208072 (corresponding U.S. Pat. No. 6,565,333), the present inventor has proposed a dispenser in which a piston and a cylinder for accommodating therein the piston are driven independently of each other by using two independent linear motion means, respectively, by which a positive displacement pump is implemented.
Also, the present inventor has proposed intermittent discharge method and apparatus (Japanese Patent Application No. 2001-110945, corresponding U.S. patent application Ser. No. 10/118,156) which uses a squeeze pressure generated by abruptly changing the gap between a piston end face and its relative-movement face based on theoretical analysis performed on the dispenser structure disclosed in Japanese Patent Application No. 2000-188899. Whereas this squeeze pressure is known as a dynamic effect of hydrodynamic bearings, it is necessary for use of this squeeze pressure that the gap between the piston end face and its opposing surface be set to a narrow one, e.g., 20 to 30 μm or less.